The present invention relates to a tensairity structure with shape memory ropes.
More precisely, the present invention relates to a structural element known in the technical field as “tensairity” that introduces distinctive elements with respect to the prior art: (i) ropes in the shape-memory alloy (SMA) with superelastic (SE) and shape memory (ME) behaviours; (ii) mechanical tensioners for adjustment of the initial tension in the ropes; (iii) optionally a control apparatus (processor) is connected to electric circuits that induces variable intensity current passes through the SMA wire ropes; (iv) optionally devices for real-time monitoring of the temperature and the level of tension in the SMA ropes; (v) optionally devices for real-time monitoring of the tensairity oscillations; (vi) optionally new structural geometries capable of sustaining multidirectional static and dynamic actions.
The term “tensairity” is a registered trademark of Airlight Ltd Via Croce 1, 6710 Biasca, Switzerland presented as a new structural concept by RH Luchsinger, A. Pedretti, M. Pedretti, P. Steingruber [1,2]. The precursors and subsequent patents to this invention are numerous. In the following, patent applications are briefly listed and described, which have a relationship with the invention proposed here.
In chronological order, the first patent which couples inflatable elements connected to rigid elements to form a structure similar to a beam is U.S. Pat. No. 2,936,056 A of 1957 [3], in which the variable-length inflatable slides are described for evacuating the passengers of an aircraft. This patent has had great resonance considering the number of patents related to it presented later and the longevity of the proposed application, still used today.
In the patent U.S. Pat. No. 5,311,706 A of 1991 [4] an inflatable reticular structure is given, which may take various forms. It is constituted by a rigid skeleton delimited by sheets of Mylar forming an inflatable envelope or inflatable cylinders interconnected by rigid elements. This application has been proposed for connection of satellites or ships. The same author proposed a new patent [5] connected to the preceding, wherein the rigid skeleton of the inflatable structure is made by reinforced fiber bundles that realize cylindrical shape elements of cable type. These beams, initially flexible, contain inside thermoplastic material filaments. Once the inflatable structure has assumed the desired shape, the filaments are melted by heat sources and the various beams stiffen and form the skeleton of the inflatable structure.
In 2001 patent U.S. Pat. No. 6,463,699 B1 [6] entitled “Air beam construction using differential pressure chambers” has been filed. The application consists in an inflatable diaphragm of cylindrical shape inside which a beam is fixed which have “I”-shaped section and consists of flexible material impermeable to air. The beam with the “I”-shaped section divides the cylindrical diaphragm in four inner air chambers tubes and contains within it the compressible material (referred to as “micro bead particles or similar material”). By introducing air pressure into the four inner air chambers, the material contained in the beam is compressed and the entire structure becomes rigid.
The patent, wherein for the first time the structural concept of tensairity is claimed, is US 20060260209 [7] filed in 2004. An inflatable structure (flexible membrane) is proposed, which is made integral with a rigid element of high slenderness and able to withstand a state of compression. Around the cylindrical diaphragm, at least two tensioned elements are twisted in opposite directions, which are connected to compressed elements. The basic idea is to inflate the pneumatic element in a manner such that the elements helically wound are subject to a state of tension and the rigid element is in compression. The compressed element is also stabilized by the pneumatic element which avoids the achievement of the instability load.
US patent 20080295417 [8] of 2008 presents an assembly of at least three inflatable cylinders made integral with each other. One of the three inflatable cylinders has a length equal to about half of the other. Overall, the cylinders in pressure form an arc to be used as skeleton structures such as domes.
In 2011, Mauro Pedretti (inventor of tensairity) proposed a structural node [9] for anchoring one or more tensairity. Such a node is able to provide compression and traction to the structural components of the tensairity using non-described screws and the cables anchors are.
In WO2004/094754, a pneumatic structural element comprising a hollow body, at least two elements in traction, two caps, at least two nodes, at least one compression rod are described. The length of the traction elements of said pneumatic structural element can be varied by Δl pneumatically, hydraulically, or mechanically. An actuator or a control unit is mounted between the ends of the traction elements and a node. The tensile stress in the traction elements can be adapted to the circumstances by means of electronic control and adjustment devices. The pressure in the pneumatic elements is varied through the passage of current in the fluid contained in the same.
The traction elements in WO2004/094754 are made of steel, aluminum, or plastic material (see p.3 1.8-14). These materials do not present any of the typical properties of the shape memory materials, including the super-elastic effect and the ability to recover a pre-impressed form.
The most recent patent relating to tensairity is the U.S. Pat. No. 8,640,386 B1 [10] filed in 2012. In this patent, simply inserting in the classical tensairity (which is subject to low inflation pressure) one or more inflatable cells is proposed, that can in turn be inflated at high pressure. The basic idea is to increase the flexural stiffness of the entire structure with the above-mentioned high-pressure internal air chambers.